Rewrite mixin application handling in Fasta.

pkg/front_end/lib/src/fasta/kernel/kernel_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.kernel_builder;
 
 export 'kernel_class_builder.dart' show KernelClassBuilder;
 
 export 'kernel_enum_builder.dart' show KernelEnumBuilder;
 
 export 'kernel_field_builder.dart' show KernelFieldBuilder;
 
 export 'kernel_formal_parameter_builder.dart' show KernelFormalParameterBuilder;
 
 export 'kernel_function_type_builder.dart' show KernelFunctionTypeBuilder;
 
 export 'kernel_function_type_alias_builder.dart'
     show KernelFunctionTypeAliasBuilder;
 
 export 'kernel_named_type_builder.dart' show KernelNamedTypeBuilder;
 
 export 'kernel_library_builder.dart' show KernelLibraryBuilder;
 
 export 'kernel_mixin_application_builder.dart'
     show KernelMixinApplicationBuilder;
 
-export 'kernel_named_mixin_application_builder.dart'
-    show KernelNamedMixinApplicationBuilder;
-
 export 'kernel_procedure_builder.dart'
     show
         KernelConstructorBuilder,
         KernelFunctionBuilder,
         KernelProcedureBuilder;
 
 export 'kernel_type_builder.dart' show KernelTypeBuilder;
 
 export 'kernel_type_variable_builder.dart' show KernelTypeVariableBuilder;
 
@@ skipping 74 matching lines @@
   int i = a.fileUri.compareTo(b.fileUri);
   if (i != 0) return i;
   return a.fileOffset.compareTo(b.fileOffset);
 }
 
 bool isRedirectingGenerativeConstructorImplementation(Constructor constructor) {
   List<Initializer> initializers = constructor.initializers;
   return initializers.length == 1 &&
       initializers.single is RedirectingInitializer;
 }